[S390] define KTIME_SCALAR for 32-bit s390

32-bit s390 has efficient support for 64/32-bit conversions, define
KTIME_SCALAR to enable the use of the plain scalar nanosecond based
representation of ktime.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -121,6 +121,9 @@ config 32BIT
 	bool
 	default y if !64BIT
 
+config KTIME_SCALAR
+	def_bool 32BIT
+
 config SMP
 	bool "Symmetric multi-processing support"
 	---help---